Capacity control for refrigeration systems



April 1967 N. E. HOPKINS ETAL 3,314,246

CAPACITY CONTROL FOR REFRIGERATION SYSTEMS Filed Oct. 22, 1965 2Sheets-Sheet 1 -aH/No1/Wva1s 591 "an /wv2.Ls 59'! 01 o oog'os ooeozO0.0'OI o (D I! I 2 'T o 3 l- IL 2 Au no" 0 m m nz m D H.

CENTRiFUGAL MAMKIM! 1 E al Dx i u ITYT. INVENTORS BY Maw ATTO R N EYApril 1957 N. E. HOPKINS ETAL 5 CAPACITY CONTROL FOR REFRIGERATIONSYSTEMS Filed Oct. 22, 1965 2 Sheets-Sheet 2 mokqmmzmo mmmzmo 20o aummuomm/a mmww l m wwww uPEumZmO HH I I I I $5538 S NQ n m WK ATTO l2 NEY United States Patent C 3,314,246 CAPACITY CONTROL F OR REFRIGERATIONSYSTEMS Neil E. Hopkins and Robert F. Muhleman, York, Pa., assignors toBorg-Warner Corporation, Chicago, 111., a corporation of Illinois FiledOct. 22, 1965, Ser. No. 500,797 4 Claims. c1. 62101) This inventionrelates generally to absorption refrigeration systems, and moreparticularly to means for diluting the absorbent solution withrefrigerant for the purposes of producing a fast acting capacity controlmeans, preventing possible evaporator freezing or solutioncrystallization, and obtaining certain operating advantages when suchabsorption systems are combined with steam turbine driven refrigerationunits wherein high pressure steam is first fed to the steam turbine andthen to the absorption machine (or machines).

A principal object of the present invention is to provide an automaticmethod of capacity reduction with a speed of response so rapid that itis practically instantaneous, in contrast to the very sluggish responsebehavior of conventional capacity control systems.

Another object of this invention is to provide first capacity reduction,without shutting down the absorption machine, the purpose being tosatisfy any safety control requirements wherein crystallization orfreeze-up is threatened, while still maintaining some capacity asrequired by the load.

A further object of this invention is to provide a combination systemincluding an absorption machine and a steam turbine driven centrifugalcompressor system with capacity control means permitting a reduction inthe capacity of the absorption system independent of the capacity of theturbine-centrifugal system to insure a better load balance between thetwo systems.

The further object of this invention is to provide a capacity control tosatisfy any condition which calls for capacity reduction.

A further object of this invention is to provide an improved controlsystem for a combined steam turbine driven centrifugal and absorptionsystem which permits the absorption machines to operate as condenser forthe steam exhausted from the turbine under load conditions below whichthe compressor would otherwise operate in an unstable region.

Still another object of the invention is to provide a system which cansatisfy a need for fast acting capacity reduction, without the ordinarynuisance of complete system shutdown and the subsequent need forrestarting.

Additional objects and advantages will be apparent from reading thefollowing detailed description taken in conjunction with the drawings,wherein:

FIGURE 1 is a schematic representation of an absorption refrigerationsystem embodying the present invention;

FIGURE 2 is a typical performance diagram of a combined absorption andsteam turbine driven centrifugal system which shows the refrigeratingcapacity of the combined system at various loads, the steam consumptionrate, and the pounds of steam used per hour for each ton ofrefrigeration; and

FIGURE 3 is a schematic diagram of a combined absorption and steamturbine driven centrifugal system and the controls therefor.

It should be pointed out that one aspect of the invention concernsapparatus and method for rapidly diluting the absorbent solution toeffect an almost instantaneous reduction in capacity, primarily for thepurpose of safety, i.e. to prevent crystallization of solution,evaporator freeze-up, etc. This concept is applicable to all types of3,3142% Patented Apr. 18, 1967 absorption systems and can therefore beused on simple absorption machines. The other aspect of the inventionconcerns the use of refrigerant to dilute the absorption solution formodulated capacity control in a combination absorption/steam-drivencentrifugal system, commonly referred to in the art as a turbo toppingsystem. It should also be understood that while this specificationoccasionally refers to the absorption system as using Water as therefrigerant and an aqueous solution of LiBr as the absorbent, there arenumerous other refrigerantabsorbent combinations to which the inventionis equally applicable.

Referring first to FIGURE 1, which is a schematic representation of anabsorption machine emboyding the principles of the invention, thedrawing shows, in general, an absorber A, an evaporator B, a generatorC, and a condenser D in a dual shell configuration, although other shellarrangements are known and could also be employed in this system. Agenerator pump E withdraws relatively dilute (59% LiBr) solution fromthe absorber and forwards it to the generator through a heat exchanger-F. Relatively concentrated (64.5% LiBr) solution flows from thegenerator through heat exchanger F to the absorber where it mixes with arelatively dilute solution to form an intermediate strength solution(61% LiBr) which is sprayed over a heat exchanger in the absorber Awhere it absorbs refrigerant (water) vapor evaporated in the evaporatorB. The absorber pump G continuously recirculates the intermediatestrength solution formed by the mixing of the concentrated solution withthe dilute solution. A refrigerant pump H withdraws liquid refrigerantfrom a pan underneath a chilled water coil J in the evaporator andcontinuously recirculates suc-h refrigerant to a spray header positionedover coil I. The dilution system to which the present invention is moreparticularly directed is shown generally at K and will be described inmore detail below.

The automatic dilution system K comprises a line 10 interconnecting therefrigerant circuit and the solution circuit to withdraw refrigerantfrom refrigerant line 12 (through which refrigerant is delivered to thespray header in the evaporator) and supply it to the absorber sprays 13.Line 10 includes an automatically controlled valve 14 which controls theflow of refrigerant from the refrigerant line to the absorber inresponse to one or more conditions. Valve 14 may be of the modulatingtype, which is responsive to a pneumatic (or equivalent electrical)control signal through line 16, or a full-flow,

no-fiow solenoid actuated valve. The modulating type is preferably usedin a turbo topping system for controlled reduction of capacity and thesolenoid type in a simple absorption machine application where thedilution system is used as a safety feature to avoid crystallization orfreeze-up. It is to be understood, however, that either type of valvemay be adapted for either system.

It is obvious that by dumping refrigerant into the solution at the pointWhere the solution is directly feeding into the absorber, the capacityis reduced rapidly. This is an important consideration because dumpingthe refrigerant into the suction line of the absorber or solution pump Gfeeding the sprays 13, or into any other point in the pipe connectionsto or from the absorber pump, will result in a substantiallyinstantaneous reduction in the concentration of solution going to theabsorption sprays. In a matter of seconds, the ability of the solutionto absorb water vapor over the absorber surface is drastically reducedwith a corresponding reduction in the reifrigera tion capacity. Thedegree of capacity reduction, of

course, depends upon the amount of refrigerant which is diverted intothe absorber for dilution purposes. If valve 14 is open to a positionallowing maximum flow, this can be sufficient to reduce the capacity ofthe system to zero if required by some unusual safety control problem.In this manner, an absorption system can be made to produce zerocapacity and at the same time utilize the same control device topartially reduce capacity, if such is the requirement.

The usual method employed in case safety controls indicate imminentfreeze-up or imminent crystallization is to completely kill the capacityby, in effect, shutting down the system. In the shutting down process,conventional systems go into a so-called dilution cycle in which certainpumps operate; but the absorption cycle is stopped either by cutting offthe condensing water flow through the absorber, discontinuing the steamsupply, or shutting off the sprays over the absorber completely. By themethod of this invention, the absorption capacity can be completelyarrested by fully opening the refrigerant dump valve, or the capacitycan be partially reduced on a modulating basis, so that the safetyconsiderations are satisfied, but not excessively so.

The point should be stressed that the solution going to the absorbersprays can be diluted very quickly to that corresponding to zerocapacity, while the main body of solution in the generator and absorbercan still be in a highly concentrated state. For example, at full load,the solution in the generator would be, say, 64.3% and the concentrationin the absorber would be, say, 59.3%. The mixture of solution going tothe sprays at full capacity, using about 40% of the solution sprayreceived from the generator, would he, say, 61.3%. This 61.3% would beflowing over the absorber and producing the full capacity condition. Nowlet us assume safety controls require a complete arrest of capacity. Bydumping sufficient refrigerant into the solution going to the absorberpump, instead of supplying 61.3% solution to the absorber sprays, theconcentration can be reduced to, say, 52%, a condition corresponding tozero capacity. This contrasts to the fact that the solutionconcentration leaving the generator would be at a relatively high levelfor some time, even though the steam valve closed immediately, due tothe flywheel capacity in the generator sump. Similarly, theconcentration of solution in the absorber pan will only reducegradually. Thus, if the controls indicate that full capacity may beresumed shortly after the safety control signal was initiated, highconcentrations still remain in the generator and absorber to be used fora quick resumption of high capacity operation.

It should be noted that there are several disclosures in the prior artwhere refrigerant is supplied to the absorber for one reason or another.In one such system described in United States Patent 2,760,350, issuedon Aug. 28, 1956, to J. R. Bourne, a line between the refrigerantcircuit and the solution circuit is opened when the system is shut downto clean out a purge line and dilute the solution in the absorber toprevent crystallization during the shutdown period. In another system,described in British Patent 658,914, issued to Carrier Engineering Ltd.on Oct. 17, 1951, an auxiliary tank is provided which is filled withrefrigerant when the system is started up, and upon shutdown therefrigerant is drained into a concentrated solution line leading to theabsorber. However, there is no suggestion that capacity can becontrolled by refrigerant supplied through an automatic valve which iscondition responsive to thereby insure safety of operation at any timethat freeze-up or crystallization is imminent.

Combination absorption and steam turbine driven dentrifugztl systemReferring now to the performance diagram shown in FIGURE 2, theoperation of a combined absorption and steam turbine driven centrifugalcompressor system will now be described. The lower portion of FIGURE 2shows the percent capacity of the system over a range from to 100% ofthe load plotted against the tons of refrigeration produced (indicatedon the left-hand ordinate) and the pounds of steam utilized (indicatedon the right-hand ordinate).

One particular problem relates to the operation of the combinationcentrifugal and lithium bromide absorption system. While the absorptionmachines can operate satisfactorily throughout a complete range ofcapacity varying all the way from absorption system load to something inthe order of 10%, the steam turbine driven centrifugal compressor systemhas certain operating limitations. Dropping from full load to partialload on the steam turbine system, one method of reducing the capacity isby gradual positioning of prerotation vanes in the compressor into amore throttled position. At a certain capacity reduction on the steamturbine driven refrigeration system, a point is reached where the systemis unstable and refrigerant flow handled by the compressor wouldoscillate badly. Operation at this condition or below would not betolerable.

At the point on FIGURE 2 designated at I, the centrifugal system isproducing approximately 1150 tons of refrigeration at 100% load andusing approximately 30,600 pounds of steam per hour. This same rate ofsteam consumption isutilized, after passing through the turbine toproduce heating for the generators in the LiBr absorption system; and at100% load, this exhaust steam will produce approximately 1510 tons ofrefrigeration for two absorption machines arranged in parallel.

Capacity modulation in the range from 100% load to approximately 44%load is controlled by varying the capacity of the centrifugal system byany number of well known methods. A common capacity control mechanismfor centrifugal compressors, as mentioned briefly above, is what isreferred to as a prerotation v-ane mechanism which comprises a pluralityof radial vanes positioned on the suction side of the compressor wheel.These vanes are movable about their radial axes and are adapted to boththrottle the flow of refrigerant and reduce the effectiveness of thecompressor by varying the angle at which the gas is introduced into thecompressor wheel. For purposes of illustration, the system to bedescribed will be considered as having a prerotation vane mechanism(PRV) for capacity control.

Capacity within the aforementioned range is controlled by the PRV unitin response to some variable, preferably the temperature of chilledwater being forwarded to the load. This also has the effect of reducingthe rate at which the exhaust steam is supplied to the LiBr absorptionunits. At approximately 44% load, steam consumption is approximately13,500 pounds per hour, indicated at point II; and this rate willproduce approximately 665 tons of absorption capacity and 505 tonsturbine capacity for a total of 1170 tons. This area of operation from100% down to 44% of maximum load is within the stable operating zone ofthe centrifugal system. Below this figure, of approximately 505 tons ofcentrifugal capacity, unstable operation would be encountered. A furtherdrop in total load, therefore, must be handled in such a way that thecentrifugal capacity is not allowed to drop. As shown in FIGURE 2, from44% to 29% of full load, the centrifugal unit is permitted to put outabout 505 tons of capacity, and the reduction in total tons is met byreducing the absorption system tonnage. However, this raises a problemwhich is One of the reasons for the use of the refrigerant dump valve.It is not possible for the lithium bromide absorption system to utilizethe amount of steam put out by the centrifugal system unless someunusual operation is developed. An important aspect of the inventionthus concerns the use of a refrigerant dump valve, so that the lithiumbromide absorption system will continue to use the amount of steamforwarded from the turbine while the capacity of the lithium bromidesystem is reduced. Consequently, from a condition of 44% total load to acondition of 29% total load, the amount of refrigerant dumped increaseson a gradual basis. Below 29% load, it is found that it is moreeconomical to shut off the centrifugal system completely and run theabsorption machines alone, either one or both as required. Thetriangular area defined within the dotted lines in FIG- URE 2 representsthe tons of refrigeration capacity dumped by diluting the solution. Asteam economy curve shown in the upper part of FIGURE 2 can beconstructed. Over the range from 100% load (I') to 44% load (11), thecombined systems are using about twelve pounds of steam per hour per tonof useful refrigeration. Between 44% load and 29% load (111'), the dumpvalve is permitted to operate to balance the two systems. The steamconsumption increases gradually to break-even point encountered at 29%load where steam consumption is then that of the absorption systems,namely 17.5 pounds steam per hour per ton. This explains, the economy ofoperation from the combination of turbo systems with absorption systems.It should be recognized that without the device, it would be necessaryto go to the absorption systems by themselves at 44% load, wherein thesteam consumption would jump immediately to approximately l7 /2 poundssteam per hour per ton. On many systems there is a further reason fornot wanting to go to the absorption systems so soon. Sometimes theabsorption systems do not have sufiicient capacity to take care of theload, and it is necessary to delay the change to the absorption systemsby themselves until a load condition well below the stable operation ofthe turbo system is reached.

The arrangement for the combined absorption and steam turbine drivencentrifugal system, and the controls therefor, are shown schematicallyin FIGURE 3. Where applicable, the same reference characters used inFIG- URE 1 will be applied to the components in FIGURE 3. The system tobe described may be generally characterized as one which employs thesteam turbine driven centrifugal system in series with two lithiumbromide absorption machines which are connected in parallel with eachother.

Chilled water returning from the load 20 is directed first to thechilled water coils in the evaporators of both absorption machine M andabsorption machine N through pump 21 and line 22 which is connected totwo parallel supply lines 23, 23' for the chilled water coils J and J.The chilled water leaves the absorption machines M and N through lines23, and 28 respectively, both of which are connected with line 32 whichleads to the chiller P in the centrifugal refrigeration system V. Thechilled water is further cooled in the chiller P and leaves through line36 to be returned to the load 20.

Cooling water for both the absorption machines and the condenser Q incentrifugal system V is supplied from a cooling tower L which includes afirst section 40 supplying the absorption machines, and a second section42 supplying the condenser Q. For the absorption machines, the coolingwater is directed from cooling tower section 40 to a pump 44 throughline 46 where it flows through line 48 to parallel lines 50 and 50supplying the absorber tube bundle (not shown) in both of the absorptionmachines. After passing through the absorbers, the cooling water is thenforwarded to the respective condensers D and D through lines 52 and 52.After passing through the condenser, the water is conducted throughlines 54 and 54 to return line 56 leading to the cooling tower. Arelatively constant temperature for the cooling water supplied to theabsorption machine is maintained by means of a temperature responsivethree-way valve 58 and a bypass line 60. If the cooling water dropsbelow a predetermined temperature as sensed by capillary bulb 62, aportion of the returning cooling water in line 56 is bypassed around thecooling tower through line 60. Cooling water for the condenser Q in thecentrifugal system is supplied by pump 64, supply line 66, and returnline 68.

The compressor R for the centrifiigal system is driven by a steamturbine S which is provided with a speed control governor 69 andsupplied from a source of high pressure steam through lines 70 and 72.After passing through the turbine, the steam is forwarded through line74, which preferably includes an override to prevent the steam pressurefrom rising above a predetermined maximum, and then through parallellines 76 and 76 to the heat exchangers in the generators C, C.Condensate from the generator is withdrawn through lines 78, 78respectively.

It will be understood that the centrifugal machine is representative ofmany types. In the one illustrated, refrigerant gas is compressed in thecompressor R and forwarded through hot gas line 80 to the condenser Q.The liquid refrigerant is withdrawn through line 82 to a receiver andintercooler 84. A portion of liquid vapor refrigerant from saidintercooler is supplied back to the compressor through line 86. Theremaining portion of the liquid refrigerant is supplied to theevaporator or cooler P through line 88 where it comes in contact with aheat exchanger 96 through which chilled water is flowing from theabsorption machines. Cold suction gas is returned to the compressorinlet through line 92.

Control of the system is maintained primarily by a temperatureresponsive element T which senses the chilled water being returned tothe load through line 36. A typical pneumatic control for such a systemis one manufactured by Johnson Service Corporation, Milwaukee, Wis. anddesignated as T900. The control unit produces a pneumatic outputpressure which is supplied both to the PRV control for compressor R andvia lines 16, 16' to valves 14, 14' in the refrigerant dump valvesystems in absorption units M, N.

The chilled water flows through the two lithium bromide machines M and Nin parallel and then through the centrifugal system V. Although thevalues for temperature and load requirements are not critical,representative values will help to illustrate the operation of thesystem. A control temperature of 39 F. is maintained by the use oftemperature control unit T If the temperature of the leaving chilledwater should start to fall below 39 F., and indicate that there has beena decrease in the cooling load, the pneumatic signal supplied to the PRVwill adjust the prerotation vanes to reduce compressor performance. As aresult, less steam goes to the absorption machines and their performanceis similarly reduced. When the prerotation vanes in the compressor reacha predetermined minimum position below which unstable compressoroperation will commence, they cannot be throttled any further because ofa limit mechanism which is previously set to establish this minimum PRVposition. This would occur, as indicated with the above reference toFIGURE 2 at a load of approximately 44%. As the temperature sensed bycontrol unit T drops still further, the control air pressure will beginto open valves 14, 14' in the refrigerant bleed or dilution system K, K.These valves will withdraw refrigerant from the discharge side of therefrigerant pumps to the suction side of the absorbent pumps and, thus,begin diluting the lithium bromide solution in the absorber. This willhave the effect of immediately reducing the refrigeration capacity ofthe absorption machines, but will have no effect on their capacity assteam condensers for the steam supplied to the generator. As thetemperature of the chilled water returning from the load approachesapproximately 43 F., a load condition occurs at which it is moreeconomical to shut down the centrifugal system entirely and continue torun with the absorption machines alone. The point at which this occursis approximately 29% of the maxim-um load. At this time, the valve 102in steam supply line 72 is closed and valve 104 between the main steamsupply and the absorption machines is opened to permit steam to flowthrough reducing valve 106 to the control valves 18, 18'.

When the turbo system is shut down, capacity is controlled by varyingthe fiow of steam to the generators C, C by means of temperature sensingelements T T responsive to the temperature of chilled Water leaving theabsorption machines for actuating control valves 18, 18'. It can,therefore, be seen that the dump valve may be used to advantage on aturbo topping system to permit operation of the steam turbine drivenrefrigeration system over a greater range of operation with the steamturbine operation limited only in the interests of economy. At the pointwhere it ,is more economical to operate lithium bromide systems alone,from the standpoint of steam consumption, then the turbo system is shutdown. At the point where unstable operation of the turbo system wouldnormally be encountered, and before the load is reduced to the pointwhere absorption systems alone would operate, the refrigerant bleedvalve is used to balance out the systems.

One other feature of the dump valve with reference to turbo toppedapplications should be mentioned. This is the very important point ofpossible safety shutdown of the lithium bromide absorption systems,which can be avoided, in many instances, by using the dump valve. Forexample, on an ordinary lithium bromide absorption system Without thedump valve, safety controls might require that the absorption system beshut down, as might be the case with low refrigerant temperatureindicated. With the dump valve in the system, the low refrigeranttemperature can signal for the dump valve to open, rather than for theabsorption systems to shut down. This permits the steam turbo system tocontinue operation with the absorption system permitted to operate andserve as a steam condenser for the steam turbine system.

By using various known control elements, such as temperature or fluidflow responsive switches, motor interlock switches, etc., a safetycontrol system may be incorporated into the absorption machines whichwill automatically activate the dilution cycle according to apredetermined sequence. A typical control sequence is illustrated in thetable below.

with a certain specific embodiment thereof, it is to be understood thatthis is by way of illustration and not by way of limitation; and thescope of this invention is defined solely by the appended claims whichshould be construed as broadly as the prior art will permit.

What is claimed is:

l. In a method for operating an absorption refrigeration machine, saidmachine comprising an evaporator, an absorber, a generator, and acondenser connected to provide a closed circuit refrigeration system,means for supplying a heating medium to said generator, a solutioncircuit including spray means in said absorber and means for circulatingabsorbent solution to said spray means, and a refrigerant circuitincluding means for circulating refrigerant to and from said evaporator,the steps including: maintaining a supply of heating medium to saidgenerator and a supply of absorbent solution to said absorber duringnormal operation throughout the entire capacity range of said system;continuously monitoring the operation of said machine to determine thepresence of an abnormal condition which is indicative of imminentsolution crystallization or evaporator freeze-up; withdrawingrefrigerant from said refrigerant circuit and supplying it to saidsolution circuit directly upstream from the absorber spray means suchthat the refrigerant mixes with the absorbent solution just prior tobeing directed into said spray means.

2. A refrigeration system comprising an absorption refrigeration machineincluding an evaporator, an absorber, a generator, and a condenser incombination with a steam turbine driven refrigeration unit including asteam turbine, a compressor, a condenser, and a chiller; means forcirculating a liquid to be chilled through said evaporator and throughsaid chiller in series; means for supplying high pressure steam [firstto said turbine and then to said generator; means for varying thecapacity of said compressor in response to varying load conditions downto a level where compressor operation is unstable; means CONTROLSEQUENCE These Results Follow- When Those Conditions Occur- SteamRel'rig. Chilled Cooling Dilution Flow 1 Solution Pump Pump Water WaterBleed Flow Flow Valve 1 Steam Flow Stops Ofi On 2 Solution Pump StopsFrom "Stop Button 3 Solution Pump Stops From Overload 4 Refrigerant PumpSteps From Overload, Chilled Water Pump Running.

5 Refrigerant Pump Stops From Overload, Chilled Water Pump Not Running.

6-.." Chilled Water Flow Stops 7 Cooling Water Flow Stops..-

Low Refrigerant Temperature Dilution Cycle 0n Off Off Dilution Cycle OffDilution Cycle On On 0 On 1 stoppage of chilled water or cooling waterflow shuts ofi steam.

- Dilution cycle controlled by timing relay which allows pump to run forpredetermined time (about 7 minutes).

Referring to the last column in the table above, it Will be apparentthat the dilution system is actuated when .any of the followingsituations occur:

(a) Solution pump stops from stop button (normal :shutdown).

(b) Refrigerant pump stops from overloadchilled Water pump running.

(c) Refrigerant pump stops from overloadchilled water pump not running.

(d) Chilled water flow stops.

(e) Cooling Water flow stops.

(f) Low refrigerant temperature.

Conditions (a) to (e) inclusive are accompanied by steam flow shut-off;but under low refrigerant temperature conditions, the steam flow iscontinued while the capacity is reduced.

While this invention has been described in connection for dilutingabsorbent solution supplied to said absorber in controlled quantities inresponse to further decreases in cooling requirements below saidunstable level; and means for discontinuing operation of said turbinedriven refrigeration unit at cooling load level within the maximumcapacity of the absorption unit.

3. In a method for operating an absorption refrigeration machine, saidmachine comprising an evaporator, an absorber, a generator, and acondenser connected to provide a closed circuit refrigeration system,means for supplying steam to said generator, a solution circuitincluding means for circulating absorbent solution to said absorber anda refrigerant circuit including means for circulating refrigerant to andfrom said evaporator, the steps including: regulating the capacity ofsaid absorption refrigeration machine by withdrawing a regulated streamof refrigerant from said refrigerant circuit and supplying saidrefrigerant to said solution circuit to dilute said solution whilecontinuing to supply steam to said generator, whereby said generatorcontinues to function as a condensing unit for the steam suppliedthereto while the capacity is being reduced.

4. An absorption refrigeration machine comprising an evaporator, anabsorber, a generator, and a condenser connected to provide a closedcircuit refrigeration system, means for supplying a heating medium tosaid generator, a solution circuit including spray means in saidabsorber and means for circulating absorbent solution 'to said spraymeans, a refrigerant circuit including means for circulating refrigerantto and from said evaporator, means for circulating a liquid to bechilled through said evaporator; means for supplying cooling water forsaid absorber and said condenser; means for transferring refrigerant insaid refrigerant circuit to said solution circuit, said last-named meansincluding a conduit connecting said refrigerant circuit to said solutioncircuit at a point just upstream from said solution spray means, valvemeans in said conduit for controlling flow between said refrigerantcircuit and said solution circuit, valve actuating means for controllingthe operation of said valve, and means for continuously monitoring theoperation of said absorption machine to determine the presence of anabnormal condition which is indicative of imminent solutioncrystallization or evaporator freeze-up to fully open said valve andpermit maximum flow of refrigerant to said absorber, said abnormalconditions including stoppage of refrigerant flow in said refrigerantcircuit, stoppage of flow of said liquid to be chilled, stoppage of flowof said cooling water supplied to said absorber or condenser, or whenthe temperature of said refrigerant or said liquid to be chilled fallsbelow a predetermined level.

References Cited by the Examiner UNITED STATES PATENTS 2,722,806 11/1955Leonard 62-489 X 2,855,765 10/1958 Smith et al. 62-494 X 2,983,1175/1961 Edberg et al. 62476 References Cited by the Applicant UNITEDSTATES PATENTS 2,760,350 8/ 195 6- Bourne.

FOREIGN PATENTS 65 8,914 10/ 1951 Great Britain.

LLOYD L. KING, Primary Examiner.

1. IN A METHOD FOR OPERATING AN ABSORPTION REFRIGERATION MACHINE, SAIDMACHINE COMPRISING AN EVAPORATOR, AN ABSORBER, A GENERATOR, AND ACONDENSER CONNECTED TO PROVIDE A CLOSED CIRCUIT REFRIGERATION SYSTEM,MEANS FOR SUPPLYING A HEATING MEDIUM TO SAID GENERATOR, A SOLUTIONCIRCUIT INCLUDING SPRAY MEANS IN SAID ABSORBER AND MEANS FOR CIRCULATINGABSORBENT SOLUTION TO SAID SPRAY MEANS, AND A REFRIGERANT CIRCUITINCLUDING MEANS FOR CIRCULATING REFRIGERANT TO AND FROM SAID EVAPORATOR,THE STEPS INCLUIDING: MAINTAINING A SUPPLY OF HEATING MEDIUM TO SAIDGENERATOR AND A SUPPLY OF ABSORBENT SOLUTION TO SAID ABSORBER DURINGNORMAL OPERATION THROUGHOUT THE ENTIRE CAPACITY RANGE OF SAID SYSTEM;CONTINUOUSLY MONITORING THE OPERATION OF SAID MACHINE TO DETERMINE THEPRESENCE OF AN ABNORMAL CONDITION WHICH IS INDICATIVE OF IMMINENTSOLUTION CRYSTALLIZATION OR EVAPORATOR CIRCUIT AND DRAWING REFRIGERANTFROM SAID REFRIGERANT CIRCUIT AND SUPPLYING IT TO SAID SOLUTION CIRCUITDIRECTLY UPSTEAM FROM THE ABSORBER SPRAY MEANS SUCH THAT THE REFRIGERANTMIXES WITH THE ABSORBENT SOLUTION JUST PRIOR TO BEING DIRECTED INTO SAIDSPRAY MEANS.